The present invention relates to pacing and defibrillation medical electrical leads. The present invention also relates to such leads adapted and configured for implantation within the coronary sinus and coronary veins.
Transvenously inserted leads for implantable cardiac pacemakers have conventionally been positioned within the right atrium or right ventricle of the patient""s heart for pacing or defibrillating the right atrium and/or right ventricle, respectively. While it is relatively safe to insert a pacing or defibrillation lead and its associated electrodes into the right atrium or right ventricle, there is a reluctance to install a similar lead in the left ventricle because of the possibility of clot formation and resulting stroke.
When a lead is implanted within a patient""s circulatory system, there is always the possibility of a thrombus being generated and released. If the lead is positioned in the right atrium or right ventricle, a generated thrombus tends to migrate through the pulmonary artery and is filtered by the patient""s lungs. A thrombus generated in the left atrium or left ventricle, however, would pose a danger to the patient due to the possibility of a resulting ischemic episode.
Thus, in those instances where left heart stimulation is desired, it has been a common practice to use an intercostal approach using a myocardial screw-in, positive-fixation lead. The screw-in lead may, however, be traumatic for the patient. There are additional instances when left ventricular pacing is desired, such as during bi-ventricular pacing. In U.S. Pat. No. 4,928,688, Mower describes an arrangement for achieving bi-ventricular pacing in which electrical stimulating pulses are applied via electrodes disposed on a single pacing lead to both the right and left ventricular chambers so as to obtain a coordinated contraction and pumping action of the heart. The ""688 patent also discloses a split pacing lead having first and second separate electrodes, wherein the first electrode is preferably introduced through the superior vena cava for pacing the right ventricle and the second electrode is introduced through the coronary sinus for pacing the left ventricle. Other electrode leads which are inserted into the coronary sinus have been described. For example, in U.S. Pat. No. 5,014,696 to Mehra and U.S. Pat. No. 4,932,407 to Williams endocardial defibrillation electrode systems are disclosed.
Still other leads and catheters have been proposed, including those described in the patents listed in Table 1 below.
As those skilled in the art will appreciate after having reviewed the specification and drawings hereof, at least some of the devices and methods discussed in the patents of Table 1 may be modified advantageously in accordance with the present invention. All patents listed in Table 1 herein above are hereby incorporated by reference herein, each in its respective entirety.
Prior art coronary vein leads for heart failure applications (i.e., pacing leads) or sudden death applications (i.e., defibrillation leads) generally must be wedged in a coronary vein to obtain a stable mechanical position and to prevent dislodgment. While such an arrangement is generally acceptable for defibrillation leads (which usually must be implanted with the distal tip thereof located near the apex of the heart), such is not the case for heart failure or pacing leads, where more basal stimulation of the heart is generally desired. Basal stimulation of the heart via the coronary vein, however, presents certain difficulties because vein diameters in the basal area of the heart are large and generally do not permit the distal end or tip of a pacing lead to be sufficiently well wedged therein.
Thus, there exits a need to provide a pacing or defibrillation medical electrical lead which is capable of being implanted within both larger diameter and smaller diameter portions of the coronary vein anatomy of a human heart where the lead does not require lead tip wedging. There is also a need to provide a medical electrical lead for pacing and defibrillation applications in which the orientation of an electrode mounted on a distal portion thereof may be controlled and adjusted to permit the electrode to point towards the left ventricular myocardium or other selected portions of the heart accessible via the coronary vein anatomy to thereby minimize pacing thresholds and improve sensing. There is a further need to provide a medical electrical lead for pacing and defibrillation applications in which the orientation of a pacing or defibrillation electrode disposed on a distal portion thereof may be determined using conventional x-ray or echo/acoustic techniques.
The present invention has certain objects. That is, the present invention provides solutions to one or more problems existing in the prior art. For example, various embodiments of the present invention have one or more of the following objects: (a) providing a medical electrical lead suitable for implantation in the coronary sinus or coronary vein which is not pushed out of the coronary sinus or coronary vein once implanted therein; (b) providing a medical electrical lead suitable for implantation within relatively large diameter portions of the coronary sinus and coronary vein without requiring wedging or the use of positive fixation means such as tines, helical screws or the like; (c) providing a medical electrical lead which exhibits enhanced removability following implantation and fibrosis; and (d) providing a medical electrical lead suitable for implantation within the coronary sinus or coronary veins which requires less time and effort to implant.
Various embodiments of the present invention suitable for implantation within the coronary sinus or coronary veins possess certain advantages, including one or more of the following: (a) exhibiting multiple lead mechanical stability points which are not dependent on any positive fixation mechanisms such as wedging, hooking, screwing or clamping; (b) providing a lead whose retention within the coronary veins is less dependent upon the particular shape or diameter of such veins than prior art leads; (c) providing a lead which permits improved pacing electrode positioning within the coronary venous anatomy; (d) providing a lead which permits lower pacing thresholds and improved sensing of intra-cardiac signals; (e) providing a lead which permits the one or more electrodes thereof to be oriented towards the myocardium or other selected portions of the heart; (f) providing a lead which exhibits improved acute and chronic pacing thresholds and sensing characteristics; (g) providing a lead which has no or reduced positive fixation mechanisms attached thereto; (h) providing a lead which may be implanted with an introducer of reduced size; (i) providing a lead which improves chronic lead removability thereof; (j) providing a straight lead which is easier, more reproducible and less expensive to manufacture; (k) providing a single pass medical electrical lead for dual chamber pacing of the left atrium and left ventricle via implantation within the coronary sinus and great cardiac vein; and (l) providing a medical electrical lead having a stiffness which varies as a function of axial distance adapted for specific placement and stability within veins other than the coronary sinus and great cardiac veins, wherein the lead exhibits appropriate distal curvature and stiffness required for implantation within the hepatic vein, spinal column, sub-cutaneously, or in other locations within the human body.
Various embodiments of the present invention exhibit one or more of the following features: (a) a distal section of a pacing or defibrillation lead having variable bending stiffness adapted and configured to create a forward driving force of the lead when the variable bending stiffness portion of the distal end of the lead is subjected to a sufficient bending moment; (b) a pacing or defibrillation lead having in a distal portion thereof a variable bending stiffness section in which the bending stiffness increases with respect to axial distance; (c) a medical electrical lead which owing to variations in bending stiffness along its axial direction imparts a positive tip force or a forward driving force to the lead, and where bending of the lead may preferentially take place along different pre-determined bending planes (e.g., three dimensional bending along multiple preferred orientations); (d) a pacing or defibrillation lead wherein variations in bending stiffness are rotationally symmetric; (e) a pacing or defibrillation lead wherein bending stiffness is rotationally asymmetric to permit orientation of one or more electrodes, fixation means, or other lead features relative to the bending plane of a bent or curved section; (f) a pacing or defibrillation lead exhibiting variable stiffness over at least distal portions thereof and which further comprises one or more of active or passive fixation features, a unipolar or multi-polar configuration, is a pacing or sensing lead, is a defibrillation lead, and/or has a combination of pacing/sensing and/or defibrillation capabilities. Methods of making, using, and implanting a lead of the present invention are also contemplated in the present invention.